Page 517 - Water and wastewater engineering

13-12 WATER AND WASTEWATER ENGINEERING

:NH -N)
Mole ratio (Cl 2
3
0.5 1.0 1.5
9
8
7 6
Residual chlorine, mg/L 5 4 Chlorine applied curve

3
Breakpoint Free
chlorine residual
2
predominant
Combined chlorine
1 residuals in predominance
1 2 3 4 5 6 7 8 9 10 11
Chlorine dosage, mg/L
FIGURE 13-2
Breakpoint chlorination. ( Source: AWWA, 1969.)

Residual chlorine, mg/L Chlorine applied Chlorine measured

Immediate demand
Chlorine dose, mg/L
FIGURE 13-3
Chlorine demand exhibited by a very fast reaction such as that with sulfur
dioxide.

Mechanisms of Disinfection
The mode of action by which disinfectants inactivate or kill microorganisms is dependent on a
large number of variables. This brief overview is limited to some of the common water disinfec-
tants and two broad classes of microorganisms: bacteria and viruses.